Hey Harmish,
it looks like your problem is exactly the same as the Yuki.
Looking inside the baxter_description at the link you provided, I see that the urdf/baxter.urdf contains the tag package:// when defining the mesh filenames.

If you want to load the model into the gzweb, it should say model://
For that, you have two options: either you change manually package by model, or you use the option -package_to_model with the urdf_spawner (as indicated by Kei Okada).